Avo Valve Tester

[Mike Watterson]

" The characteristic curves mean very little to me. "

• Needed when designing a radio or amp.
  
• Needed to decide if valve is still usable, the "pass"/"Fail" of most testers only made sense in era when new ones could be bought or to ensure new one was OK, or if doubt you'd mixed up the the stock
  
• Needed if the valve isn't listed in the valve tester's data manual or you have no data.
  
• Needed to understand how to bias for Anode Bend detector
  
• Needed to pick an Anode load for a particular HT and bias current. The 2000 Ohms or whatever is only an example. (Load line)
  
• Deciding on Screen grid or control grid ranges for AGC or Modulation.
  

It was about the first thing to do with electronics in physics that we did, plot I/V graphs for a thermionic diode and triode, though it was latter part of 1960s. No transistors in the lab at school, though I had them in my Philips EE kit from maybe Christmas 1965, (before I even went to secondary school, well a grammar school actually).

A simple go/fail test can usually be more reliably done in the equipment if the components/voltages are correct. Tektronix had an article on that. Very often valves that "fail" in simple testers are absolutely fine for many years in Vintage gear, they just don't meet maker's spec for acceptable quality for new parts!  Unlike transistors, which mostly tend to work or don't at all (though not always true) the valves gradually degrade. It depends on the exact model of radio / amp / application as to when the valve is really no use any longer!

The oldest catalogues I have of valves almost all give the curves beside the basic table of data.

P.S. One of the co-founders I knew of the Poly Radio club was doing the Marine Radio Officer course (maybe 1974).